Here they are using this information to automatically check that it is in fact you instead of having a staff member look at you and check against your passport's photo.
This is especially true for domestic travel as well.
As a US citizen, this is mostly just to validate any visa requirements for the country you're traveling to.
However, for non citizens, this data gets sent to CBP to create an exit record. I believe the concern is that between the check-in counter and the flight, you could trade places with someone to effectively overstay a visa without CBP's computer systems noticing (since you'd have a valid exit record)... hence the push for facial recognition at the gate.
At TSA, They scan the first page of passport (or local ID) and usually Full body scan. So in the strict sense of facially scanned no.
At the gate (until now), neither. They would scan the boarding pass and eyeball the passport if international.
Again the point here is that in the first two instances these are Government agencies doing the scanning. At the third, the Government no longer has anything to do with it.
The question with this stuff is how and where are Airlines (private companies) getting a database of biometric data and what are they doing with it?
Neither of which are good.
It isn’t US Boarder Control running the facial control system, its Delta, Southwest, or anyone else, which has implications about the privacy of the biometric data, that up until this point hasn’t been collected by Airlines, only Boarder entities.
That said, in order to boot strap this system, Delta et., al. would have had to either; 1. Build their own database of biometric and facial data that they believe was reliable (unlikely) 2. Get a full and continually updated copy from CBP (Probably noisy) 3. Use an API made available by CBP that acts as a Biometric/Facial oracle.
I’ve heard rumblings that it’s 3, but I can’t cite anything to back that claim up, so grains of salt.